The present disclosure relates generally to heat sinks and more particularly to heat sinks having a convex contact surface and a method of making the same. Heat sinks are used to conduct heat away from a surface of a device such as a microprocessor. Heat sinks feature a thermal face, which is in thermal communication with a device from which heat is to be conducted.
FIG. 1 depicts a conventional heat sink 10 having a thermal face 12 that is concave. In the example shown in FIG. 1, the distance d is about 25 um. Heat sink 10 includes a base 14 made from a metal (e.g., copper) having a plurality of metal (e.g., copper) fins 16 secured to the base 14. Fins 16 are positioned in grooves 18 and secured to base 14 by solder 20 which is a Pb—Sn solder.
FIGS. 2a–2d illustrate the manufacturing process for heat sink 10 of FIG. 1. The upper portion of base 14 including grooves 18, solder 20 and a portion of base 14 is represented as region 22 for convenience of illustration. FIG. 2a depicts heat sink 10 heated above a melting temperature of Pb—Sn solder 20. Fins 16 are then placed in solder 20 in grooves 18. The heat sink 10 is then cooled to room temperature as shown in FIG. 2b. Due to the differing coefficients of thermal expansion (CTE) between solder 20 and base 14, the solder 20 goes into tension and the base 14 goes into compression. The CTE of the solder 20 is about 25 ppm/C and the CTE of the copper base 14 and copper fins 16 is about 17 ppm/C.
The thermal face 12 is then machined to be planar as shown in FIG. 2c. Over time, the tensile stresses in solder 20 relieve and solder 20 stretches. The compressive stresses in copper base 14 relieve over time and the copper base 14 shrinks. This results in thermal face 12 being concave as shown in FIG. 2d. The concavity of thermal face 12 results in reduced contact between the heat sink 10 and the surface from which heat is to be transferred and poor heat transfer performance.